/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jacky.lanlan.song.web;

import java.util.HashMap;
import java.util.Map;

/**
 * A simple parser intended to parse sequences of name/value pairs. Parameter
 * values are exptected to be enclosed in quotes if they contain unsafe
 * characters, such as '=' characters or separators. Parameter values are
 * optional and can be omitted.
 * 
 * <p>
 * <code>param1 = value; param2 = "anything goes; really"; param3</code>
 * </p>
 * 
 * @author <a href="mailto:oleg@ural.ru">Oleg Kalnichevski</a>
 */

public class ParameterParser {
	/**
   * String to be parsed.
   */
	private char[] chars = null;

	/**
   * Current position in the string.
   */
	private int pos = 0;

	/**
   * Maximum position in the string.
   */
	private int len = 0;

	/**
   * Start of a token.
   */
	private int i1 = 0;

	/**
   * End of a token.
   */
	private int i2 = 0;

	/**
   * Whether names stored in the map should be converted to lower case.
   */
	private boolean lowerCaseNames = false;

	/**
   * Default ParameterParser constructor.
   */
	public ParameterParser() {
		super();
	}

	/**
   * Are there any characters left to parse?
   * 
   * @return <tt>true</tt> if there are unparsed characters, <tt>false</tt>
   *         otherwise.
   */
	private boolean hasChar() {
		return this.pos < this.len;
	}

	/**
   * A helper method to process the parsed token. This method removes leading
   * and trailing blanks as well as enclosing quotation marks, when necessary.
   * 
   * @param quoted
   *          <tt>true</tt> if quotation marks are expected, <tt>false</tt>
   *          otherwise.
   * @return the token
   */
	private String getToken(boolean quoted) {
		// Trim leading white spaces
		while ((i1 < i2) && (Character.isWhitespace(chars[i1]))) {
			i1++;
		}
		// Trim trailing white spaces
		while ((i2 > i1) && (Character.isWhitespace(chars[i2 - 1]))) {
			i2--;
		}
		// Strip away quotation marks if necessary
		if (quoted) {
			if (((i2 - i1) >= 2) && (chars[i1] == '"') && (chars[i2 - 1] == '"')) {
				i1++;
				i2--;
			}
		}
		String result = null;
		if (i2 > i1) {
			result = new String(chars, i1, i2 - i1);
		}
		return result;
	}

	/**
   * Tests if the given character is present in the array of characters.
   * 
   * @param ch
   *          the character to test for presense in the array of characters
   * @param charray
   *          the array of characters to test against
   * 
   * @return <tt>true</tt> if the character is present in the array of
   *         characters, <tt>false</tt> otherwise.
   */
	private boolean isOneOf(char ch, final char[] charray) {
		boolean result = false;
		for (int i = 0; i < charray.length; i++) {
			if (ch == charray[i]) {
				result = true;
				break;
			}
		}
		return result;
	}

	/**
   * Parses out a token until any of the given terminators is encountered.
   * 
   * @param terminators
   *          the array of terminating characters. Any of these characters when
   *          encountered signify the end of the token
   * 
   * @return the token
   */
	private String parseToken(final char[] terminators) {
		char ch;
		i1 = pos;
		i2 = pos;
		while (hasChar()) {
			ch = chars[pos];
			if (isOneOf(ch, terminators)) {
				break;
			}
			i2++;
			pos++;
		}
		return getToken(false);
	}

	/**
   * Parses out a token until any of the given terminators is encountered
   * outside the quotation marks.
   * 
   * @param terminators
   *          the array of terminating characters. Any of these characters when
   *          encountered outside the quotation marks signify the end of the
   *          token
   * 
   * @return the token
   */
	private String parseQuotedToken(final char[] terminators) {
		char ch;
		i1 = pos;
		i2 = pos;
		boolean quoted = false;
		boolean charEscaped = false;
		while (hasChar()) {
			ch = chars[pos];
			if (!quoted && isOneOf(ch, terminators)) {
				break;
			}
			if (!charEscaped && ch == '"') {
				quoted = !quoted;
			}
			charEscaped = (!charEscaped && ch == '\\');
			i2++;
			pos++;

		}
		return getToken(true);
	}

	/**
   * Returns <tt>true</tt> if parameter names are to be converted to lower
   * case when name/value pairs are parsed.
   * 
   * @return <tt>true</tt> if parameter names are to be converted to lower
   *         case when name/value pairs are parsed. Otherwise returns
   *         <tt>false</tt>
   */
	public boolean isLowerCaseNames() {
		return this.lowerCaseNames;
	}

	/**
   * Sets the flag if parameter names are to be converted to lower case when
   * name/value pairs are parsed.
   * 
   * @param b
   *          <tt>true</tt> if parameter names are to be converted to lower
   *          case when name/value pairs are parsed. <tt>false</tt> otherwise.
   */
	public void setLowerCaseNames(boolean b) {
		this.lowerCaseNames = b;
	}

	/**
   * Extracts a map of name/value pairs from the given string. Names are
   * expected to be unique.
   * 
   * @param str
   *          the string that contains a sequence of name/value pairs
   * @param separator
   *          the name/value pairs separator
   * 
   * @return a map of name/value pairs
   */
	public Map<String,String> parse(final String str, char separator) {
		if (str == null) { return new HashMap<String,String>(); }
		return parse(str.toCharArray(), separator);
	}

	/**
   * Extracts a map of name/value pairs from the given array of characters.
   * Names are expected to be unique.
   * 
   * @param chars
   *          the array of characters that contains a sequence of name/value
   *          pairs
   * @param separator
   *          the name/value pairs separator
   * 
   * @return a map of name/value pairs
   */
	public Map<String,String> parse(final char[] chars, char separator) {
		if (chars == null) { return new HashMap<String,String>(); }
		return parse(chars, 0, chars.length, separator);
	}

	/**
   * Extracts a map of name/value pairs from the given array of characters.
   * Names are expected to be unique.
   * 
   * @param chars
   *          the array of characters that contains a sequence of name/value
   *          pairs
   * @param offset -
   *          the initial offset.
   * @param length -
   *          the length.
   * @param separator
   *          the name/value pairs separator
   * 
   * @return a map of name/value pairs
   */
	public Map<String,String> parse(final char[] chars, int offset, int length, char separator) {

		if (chars == null) { return new HashMap<String,String>(); }
		Map<String,String> params = new HashMap<String,String>();
		this.chars = chars;
		this.pos = offset;
		this.len = length;

		String paramName = null;
		String paramValue = null;
		while (hasChar()) {
			paramName = parseToken(new char[] { '=', separator });
			paramValue = null;
			if (hasChar() && (chars[pos] == '=')) {
				pos++; // skip '='
				paramValue = parseQuotedToken(new char[] { separator });
			}
			if (hasChar() && (chars[pos] == separator)) {
				pos++; // skip separator
			}
			if ((paramName != null) && (paramName.length() > 0)) {
				if (this.lowerCaseNames) {
					paramName = paramName.toLowerCase();
				}
				params.put(paramName, paramValue);
			}
		}
		return params;
	}
}
